如何在android中使用显示指标动态设置imageview的边距

嗨，我在做一个适用于所有尺寸的应用程序。在这里，我使用显示指标显示imageview，如果在xml文件中拍摄imageview，我的代码适用于所有大小，但如果我当时动态拍摄imageview，同时提供边距，我会遇到异常，您有人能帮我吗

my code:

         ImageView I2=(ImageView)findViewById(R.id.caption);
                     captionbitmap=BitmapFactory.decodeStream(getResources().openRawResource(R.drawable.practise));

          captiondrwable = new BitmapDrawable(captionbitmap); 
             I2.setBackgroundDrawable(captiondrwable);
   RelativeLayout.LayoutParams layoutcap= (RelativeLayout.LayoutParams) I2.getLayoutParams();      
             layoutcap.height=(int)(50*(screenHeight/600));  
             layoutcap.width=(int)(80*(screenWidth/1024));
             layoutcap.topMargin=(int)(50*(screenHeight/600)); 
             layoutcap.leftMargin=(int)(15*(screenWidth/1024));
       // above   code working well for all sizes



            ImageView I2=new ImageView(this);

          captionbitmap=BitmapFactory.decodeStream(getResources().openRawResource(R.drawable.practise));

          captiondrwable = new BitmapDrawable(captionbitmap); 
             I2.setBackgroundDrawable(captiondrwable);
   RelativeLayout.LayoutParams layoutcap= (RelativeLayout.LayoutParams) I2.getLayoutParams();      
             layoutcap.height=(int)(50*(screenHeight/600));  
             layoutcap.width=(int)(80*(screenWidth/1024));
             layoutcap.topMargin=(int)(50*(screenHeight/600)); 
             layoutcap.leftMargin=(int)(15*(screenWidth/1024));


    // above imageview i gave dynamically that my code is not working so pls any one give me any        idea

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能否显示定义第一个ImageView的XML？但我的xml代码运行得很好，当时我动态地给出imageview时遇到了问题